1. Field of the Invention
The present invention relates to a network device in a packet switched network and more particularly to a method of throttling a memory management unit and of ensuring that information being sent to the memory management unit from an external memory is correct.
2. Description of the Related Art
A packet switched network may include one or more network devices, such as a Ethernet switching chip, each of which includes several modules that are used to process information that is transmitted through the device. Specifically, the device includes an ingress module, a Memory Management Unit (MMU) and an egress module. The ingress module includes switching functionality for determining to which destination port a packet should be directed. The MMU is used for storing packet information and performing resource checks. The egress module is used for performing packet modification and for transmitting the packet to at least one appropriate destination port. One of the ports on the device may be a CPU port that enables the device to send and receive information to and from external switching/routing control entities or CPUs.
As packets enter the device from multiple ports, they are forwarded to the ingress module where switching and other processing are performed on the packets. Thereafter, the packets are transmitted to one or more destination ports through the MMU and the egress module. The MMU enables sharing of packet buffer among different ports while providing resource guarantees for every ingress port, egress port and class of service queue. According to a current switching system architecture, as packets are stored by the MMU the packets may be dynamically stored in one or more memory locations on external memory devices. To retrieve information from the external memory device, the MMU sends a command to the MCU which translates the command into instructions that can be processed by the external memory device. According to a current device, the MMU may request access from up to 16 banks of the external memory device. Multiple simultaneous large requests, however, cause latency problems in the network device. Therefore, a system and method is needed to minimize latency issues.